1. Field of the Invention
The present invention generally relates to a communication connection bypass method and to nodes and servers both of which implement the method. More particularly, the present invention relates to an improvement in minimizing loss of traffic flowing through a communication connection established in a connection-oriented network, in case of a node or link failure on the communication connection.
2. Description of the Related Art
Conventionally, such a communication connection bypass system has been used for the following purpose. In case of a node or link failure on a communication connection (main communication connection) in a connection-oriented network, a need exists for minimizing loss of the traffic flowing through the failed communication connection. This is implemented by switching a data transfer route to a pre-established backup communication connection that bypasses the failed node or link.
One example of known communication connection bypass systems is disclosed in Internet Draft, draft-gan-fast-reroute-00.txt, April 2001. In this document, a method for establishing backup label switched paths (hereinafter referred to as “LSPs”) in a multi-protocol label switching network (hereinafter referred to as a “MPLS network”) is proposed. The term “backup LSP” refers to an LSP that is switched from an LSP (main LSP) to bypass a failure in case of a link or node failure on the main LSP.
FIG. 1 is a schematic diagram to illustrate a method for establishing backup LSPs proposed in the document. In FIG. 1, label switching routers (hereinafter referred to as “LSRs”) 101 to 108 are provided in a network. The LSR 101 to 108 are interconnected by links 201 to 211.
In FIG. 1, a main LSP 301 is established with the LSR 101 being the ingress LSR and the LSR 105 being the egress LSR. In this case, as backup LSPs, backup LSPs 302 to 305 are established. That is, the backup LSPs 302 to 305 are respectively established such that the LSRs 101 to 104, which are on the main LSP 301, function as the starting points, namely, the starting nodes. Each backup LSP is also established to be directed to an LSR that is two hops or more away downstream from a starting node LSR, so as to bypass an adjacent downstream link or node. When, however, the LSR 104 is the starting node, the backup LSP 305 is established so as to bypass the adjacent downstream link 204 since the LSR one hop away downstream from the LSR 104 is the egress LSR. Each backup LSP bypasses a failure at a downstream link or node, which is on the backup LSP, adjacent to an LSR that serves as the starting node for the backup LSP. The backup LSPs 302, 303, 304, and 305 merge into the main LSP 301 at the LSRs 103, 104, 105, and 105, respectively. For example, traffic flowing on the backup LSP 302 merges into the main LSP 301 at the LSR 103.
Thus, pre-establishing the backup LSPs 302 to 305 in this manner eliminates the need for reestablishing an LSP for bypassing a failed link or node in case of a failure. In addition, even when any link or node between the LSRs 101 and 105 on the main LSP 301 has failed, an upstream LSR adjacent to the failed link or node can detect the failure and switch over to a backup LSP originating from the LSR that has detected the failure.
That is, when an LSR on the main LSP detects a failure of an adjacent downstream link or node, the LSR immediately switches from the main LSP to a backup LSP originating from the LSR that has detected the failure, without notifying other nodes of the failure. This can achieve failure recovery.
However, the communication connection bypass system described above has some disadvantages.
The first disadvantage is as follows. Since a backup communication connection is set up independently from each node on a main communication connection, the backup communication connection consumes a large amount of link resources. This is because a backup communication connection must be established to be node-disjoint from the segment on the main communication connection to be protected by the backup communication connection. Thus, the amount of link resources consumed per backup communication connection tends to be large. Additionally, since the backup communication connection is set up from each node except the egress node of the main communication connection, the number of backup communication connections increases in proportion to the number of hops on the main communication connection. For example, in FIG. 1, the main LSP 301 consumes link resources corresponding to four links. In contrast, the backup LSPs 302 to 305 consume link resources corresponding to 12 links in total.
The second disadvantage is as follows. When a plurality of main communication connections are set up between two given nodes in a network to provide traffic load balancing, the setup of backup communication connections for each main communication connection for load balancing results in the backup communication connections consuming a large amount of link resources. This is because the backup communication connections are set up independently from the main communication connections protected by the backup communication connections. Consequently, when the backup communication connections are set up for each main communication connection for load balancing, the total amount of link resources that are consumed by the backup communication connections increases in proportion to the number of the main communication connections.